With a structural volume of 96 square kilometers, the Fort Peck dam in Montana is the second largest dam in the world, and one of the most incredible largest dam in the world. It is built alongside six other dams on the river Missouri and is the largest among them. Its reservoir creates the fifth largest man-made lake in the US- The Fort Peck Lake. It is also the longest dam in the world.After seven years of repeated failures and reconstructions, the Fort Peck dam was finally completed in 1940. It is a must visit!How to reach: You can take Highway 117 and 15 Miles South from US-2. The nearest town is Nashua.